A conventional syringe pump system for aspirating and dispensing volumes of liquid includes a syringe mounted vertically or horizontally on a syringe pump with a drive means detachable coupled to a plunger emanating from a bottom or rearward end of a chamber of the syringe and a rotary valve detachable coupled to a top or forward end of the syringe in open communication with the chamber.
The rotary valve typically includes a stationary passageway in open communication with both the syringe chamber and a rotatable passageway extending through a rotatable valve member of the rotary valve for providing open communication between the syringe chamber and an inlet port of the valve or an outlet port of the valve as selected by the position of the rotatable valve member. An inlet fluid line typically couples the inlet port to a first reservoir of fluid while an outlet fluid line typically couples the outlet port to a second reservoir or a subsequent conventional syringe pump system for dispensing fluid thereto.
For aspirating fluid, the conventional syringe pump system rotates the rotatable valve member to provide open fluid communication between the syringe chamber and the first reservoir of fluid and then draws the plunger downward for aspirating fluid into the syringe chamber from the first reservoir of fluid. For dispensing fluid, the conventional syringe pump system rotates the rotatable valve member to provide open fluid communication between the syringe chamber and the second reservoir and then drives the plunger upward for dispensing fluid from the syringe chamber to the second reservoir or to the subsequent conventional syringe pump system thereby completing one syringe pump cycle.
Although the aim of mounting the syringe vertically is to help remove air from the syringe as air bubbles rise naturally towards the rotary valve during use, there is an inherent problem with the conventional syringe pump system in that the stationary passageway of the rotary valve creates and defines a dead volume in the system where air becomes trapped and unable to exit therefrom.
For example, when the plunger is at the top of its stroke, the air in the syringe is pushed into the dead volume defined by the stationary passageway and then when the syringe is refilled, because the refilling occurs through the same stationary passageway, the trapped air is pushed back into the syringe ahead of the inflowing fluid. As a result of the fact that the air is much more easily compressed than the liquid to be pumped, air bubbles in the syringe can cause the performance to be reduced to a level at which accuracy and reliability of pumping of the liquid is unacceptable.
In particular, each conventional syringe pump system undergoes an initialization process for priming the system which serves the purpose of completely filling the input fluid line up to the syringe with one or more user selected fluids. When the fluid first reaches the valve, the syringe draws in both fluid and air causing the fluid to foam or froth within the chamber of the syringe. Then, the rotatable valve member is turned and the plunger is actuated in an effort to dispense or push the fluid and air out of the outlet port of the valve. An impediment to this effort comes about as a result of the plunger pushing air from the syringe into the dead volume defined by the stationary passageway where it becomes trapped and unable to exit therefrom. Thus, when the valve member is turned back to communicate the syringe chamber with the first reservoir of fluid and the plunger is again actuated the air that was previously trapped in the dead volume is drawn back into the syringe ahead of the inflowing fluid thereby resulting in additional strokes for initially priming the conventional syringe pump system for obtaining a solid train of fluid flowing through the syringe. Hence, these additional strokes result in both time and fluid consumption which both can be costly and in short supply.
Another problem that is common in conventional syringe pump systems is the diminishing return or dilution over time during a purging process such as is associated with switching from a first fluid to a second different fluid.
For example, the purging process of the conventional syringe pump system includes aspirating or drawing both a first remaining fluid and a second different fluid into the syringe chamber where the fluids mix. Subsequently, this fluid mixture is dispensed out of the syringe by rotating the rotatable valve member to communicate the syringe chamber with the outlet port of the valve and then actuating the plunger for dispensing the fluid mixture out of the outlet port. Although fluid mixture is dispensed from the outlet port of the valve, a portion of the fluid mixture remains trapped within the dead volume of the valve defined by the stationary passageway. Thus, when the rotatable valve member is turned back to communicate the syringe chamber with the inlet port of the valve both the fluid mix remaining within the dead volume of the valve and fluid in the inlet fluid line is aspirated into the syringe chamber thereby having a diminishing return or dilution of the fluid drawn from the inlet fluid line. Hence, this results in the need for additional strokes for purging the conventional syringe pump system of fluid thereby resulting in both time and fluid consumption which both can be costly and in short supply.
A further problem associated with conventional syringe pump systems is with respect to the out gassing that is linked with running fluids through conventional syringe pump systems.
Particularly, a user fluid that is ran through the conventional syringe pump system has a small amount of gas that can degas and turn into bubbles because, by its nature, the syringe in the syringe pump system is reducing and pressurizing the fluid. When the pressure on the fluid is reduced, the bubbles out gas and turn into bubbles that tend to stay in the syringe or dead volume of the valve and stubbornly stick to the sides thereof.
The significant shortcomings as described above also apply to valves that employ a method of switching or opening and closing flow paths inside of the valve by means other than a rotary action.
Moreover, an additional dead volume contributing to the problems described above may be found in the tip of the conventional syringe.
Hence, there is a need to overcome the significant shortcomings of the known prior-art as delineated hereinabove.